The present disclosure sets out an improved variable load mechanism for use in a valve which seals the flow of a switched fluid by operation of the valve. The flow passes through the mechanism in a region which involves shear seal surfaces. These surfaces tend to wear with loading of the two members defining that switching mechanism. For sake of brevity, this will be defined as a moveable valve element cooperative with a valve body. There is relative motion between the two which must be accomplished, and this is accomplished under load.
As set forth in an earlier patent of the present inventor which is U.S. Pat. No. 4,550,742, a variable loading system for a shear seal valve mechanism was defined. In particular, that shows a variable load which is applied to the valve element.
This disclosure sets out a shear seal system useful in switching fluid flow. Especially where the fluid flow is subject to pressure peaks, this system is well able to accommodate fluctuations in the input pressure. Moreover, this system comprises a valve element which is spring loaded by a stack of Beliville washers which provide a controllable first force on the valve element. A second force is added for the valve element. The second force is hydraulically powered so that it increases or decreases with pressure. There is an input pressure chamber which adds a second force applied to the valve element thereby increasing the loading on the seals. The significance of this and its mode of operation will be given below. In general terms, the valve element and cooperative valve seat operate in a dry condition without liquid sealants. The element and seal involve a seal which prevents leakage out of that region. The seal is forced to operate in a dry condition because solvents and lubricants cannot be introduced into the region of the seal. Otherwise, they would mix with the switched fluids and thereby commingle with the switched fluid flow. Because this is involved in testing equipment, the quantities are small and any comingling of lubricant will create serious data distortion reported by test equipment connected to the valves of the present disclosure. Constant pressure applied to the valve element is not needed. Rather, the pressure for the seal is varied as much as possible to yet still obtain a safe and leak proof operation. As taught in the earlier disclosure, and especially referring to FIG. 2 thereof, the forces acting on the valve element assure a leak proof operation. They are made variable dependent on the pressure of fluid applied to the valve which prompts the valve element to vary loading and hence fluctuates with fluctuations in pressure. The loading occasioned by input pressure variations in the previous structure is dependent on the requirements to prevent leakage and that is dependent on the pressure of fluid which is to be switched.
That valve construction is quite successful. There is a limitation, however, on the life of the components. The present disclosure seeks to extend the life of the components by limiting somewhat the range of excursion in response to valve seat forces. In this version of equipment, the valve element is provided with a first force from a stack of Bellville washers. This spring force is defined by the geometry of the springs. The present system contemplates a first and fixed spring force acting on the valve element assisted by a second force acting on the valve element through the spring which is pressure fluid determined driven. The second force, however, has a limit which is implemented by control of valve element excrusion. More specifically, the valve element in this construction is a rotary valve element mounted on a stem or shaft. The stem is constructed so that a surrounding shoulder is confronted by the Bellville springs thereby confining the springs around the stem of the valve element. This applies the first or spring driven force against the valve element. In addition to that, the stem includes appropriate surrounding seals to define a pressure receiving chamber. The chamber is an annular chamber around the stem and enables a seal member to move in telescoping fashion in the chamber. In response to pressure fluid applied to it, the stem is moved, but its range of movement is limited by a set of interlocking shoulders. This therefore, limits the traverse or travel of the stem so that the range of travel is also limited. Moreover, when travel does occur in response to pressure fluid, it is implemented by pushing against the lower end of the Bellville spring. This adds the hydraulically originated force under the spring, and imparts more force to the same stem mounted valve element.
As will be explained in the description below, this mode of operation changes the loading of the valve element on the valve seat and therefore extends the life. Moreover, by providing this limit on the range of travel, overloading is prevented.